Tire with rubber tread of intermedial and lateral zones with path of least electrical resistance

ABSTRACT

The invention relates to a tire having a rubber tread of a circumferentially zoned tread. The tread zones are comprised of three circumferential load bearing zones, with each zone containing a portion of the running surface of the tread, comprised of a silica-rich intermedial rubber zone positioned between and extending beneath two carbon black-rich lateral tread zones. The tread configuration contains an underlying carbon black-rich base rubber layer. The intermedial and stratified lateral zones are comprised of rubber compositions having differentiated rebound physical properties. A path of least electrical resistance extends from a lateral carbon black-rich rubber tread zone to the carbon black-rich tread base layer by an extension of a lateral tread zone or by an intermediate carbon black-rich rubber bridge.

The invention relates to a tire having a rubber tread of acircumferentially zoned tread. The tread zones are comprised of threecircumferential load bearing zones, with each zone containing a portionof the running surface of the tread, comprised of a silica-richintermedial rubber zone positioned between and extending beneath twocarbon black-rich lateral tread zones. The tread configuration containsan underlying carbon black-rich base rubber layer. The intermedial andstratified lateral zones are comprised of rubber compositions havingdifferentiated rebound physical properties. A path of least electricalresistance extends from a lateral carbon black-rich rubber tread zone tothe carbon black-rich tread base layer by an extension of a lateraltread zone or by an intermediate carbon black-rich rubber bridge.

BACKGROUND FOR THE INVENTION

Tire treads for pneumatic tires typically have running surfaces of aunitary rubber composition and therefore rubber properties attributed tothe tread rubber composition across the face of the tread. The tread isusually composed of a lug and groove configuration composed ofground-contacting lugs with intervening grooves between the lugs.

Tires intended for heavy duty, in a sense of carrying large loads, suchas for example truck tires, are typically intended to experienceinternal heat generation during the service, or operation, of the tireand to experience considerable stress at lateral, portion(s) of thetread, including tread grooves contained in the tread'sground-contacting lateral tread zones due to, for example, vehicularcornering and tire scuffing against roadside objects including, forexample, roadside curbs. When such tire stress is excessive, a surfacecracking of a surface of a groove wall contained in a stratified lateralzone of the tread may occur in response to the considerable stress.

The outer, ground-contacting, tread cap rubber layer is typicallycomprised of a relatively low hysteretic rubber composition to promoterelatively low internal heat generation as the tire is used in serviceas evidenced by relatively high rubber rebound and relatively low tandelta physical properties to, in turn, thereby promote a low rollingresistance of the tire tread as well as extended tread shoulder groovedurability.

For this invention, it is proposed to provide the outer tread cap rubberlayer in a form of circumferential zones of significantly differentphysical properties, particularly rubber compositions of differingphysical properties such as hot rebound (100° C.) properties which areindicative of hysteresis of the rubber composition and predictive ofrate of internal heat generation during use of the tire and alsopredictive of rolling resistance of the tire. For this invention, suchtread zones are provided as a silica-rich intermedial rubber zone topromote lower hysteresis with resultant lower internal heat build-upacross a major portion of the breadth of the tire tread positionedbetween and underlying carbon black-rich lateral tread rubber zones.

In particular, it is proposed to provide the silica-rich intermedialrubber zone, which extends across a major portion of the carbon blackrich underlying tread base rubber layer, with a higher 100° C. hotrebound property, thereby a lower hysteresis property, than theoverlying carbon black-rich lateral tread rubber zones to promote arelative maximization of reduced internal heat build-up within thetread. The lateral tread zone rubber composition is therefore proposedto have a relatively lower 100° C. hot rebound property, thereby ahigher hysteresis. It is further desired for the lateral tread zonerubber composition to have a greater or equal, preferably greater tearresistance property compared to the intermedial tread zone rubber,particularly to reinforce tread grooves contained in the stratifiedlateral tread zones.

Historically, tires have heretofore been proposed having an outersurface composed of a plurality of circumferential zones of rubbercompositions to promote various properties for the tread's runningsurface.

For example, see U.S. Pat. Nos. 8,662,123; 7,789,117; 7,559,348;7,131,474 and 6,959,744; Patent Publication Nos. 2007/0017617 and2009/0107597; and EP0718127, EP0798142 and DE19812934.

However, it is hereby proposed to provide a tire with tread containing acombination of circumferential intermedial and lateral zones of rubbercompositions to promote significantly differentiated physical propertiesto include rebound properties to therefore promote differentiatedhysteresis properties. The higher rebound property (e.g. lowerhysteresis property) for the tread intermedial zone layer, as comparedto the lateral tread zone layer, is desired to promote, or maximize, abeneficially lower internal heat build up for the tread.

In this manner then, the central portion of the tread is a dual layeredcomposite of an intermedial tread cap rubber zone layer and tread baserubber layer. The lateral portions of the tread are triple layeredcomposites of the lateral tread rubber zones, the portion of theintermedial tread zone which extends beneath and underlies the lateraltread zones and the tread base rubber layer which underlies theintermedial tread zone.

The tire tread it thereby comprised of a cooperative layered compositeof the aforesaid circumferential rubber layers.

In one embodiment, tread grooves are contained in both the intermedialtread zone and the lateral tread zones. By providing the lateral treadzone rubber layers with a tear resistance property, it is intended thattear resistance of the surface of the grooves contained in the lateralportion of the tread is promoted.

In the description of this invention, the terms “rubber” and “elastomer”may be used interchangeably, unless otherwise provided. The terms“rubber composition,” “compounded rubber” and “rubber compound” may beused interchangeably to refer to “rubber which has been blended or mixedwith various ingredients and materials” and such terms are well known tothose having skill in the rubber mixing or rubber compounding art. Theterms “cure” and “vulcanize” may be used interchangeably unlessotherwise provided. The term “phr” may be used to refer to parts of arespective material per 100 parts by weight of rubber, or elastomer.

SUMMARY AND PRACTICE OF THE INVENTION

In accordance with this invention, a tire is provided having acircumferential rubber tread composed of a cap/base configurationcomprised of an outer tread cap rubber layer with a lug and grooveconfiguration with the outer portions of the tread lugs providing therunning surface of the tread, and a tread base rubber layer underlyingthe outer tread cap rubber layer;

wherein the outer tread cap rubber layer is composed of threecircumferential load bearing zones comprised of a silica-richintermedial tread zone rubber layer positioned between and extendingbeneath two carbon black-rich lateral tread zone rubber layers tothereby underlie the lateral tread zone rubber layers and overlay thecarbon back-rich tread base rubber layer;

wherein outer tread lug surfaces of the intermedial tread zone rubberlayer and the lateral tread zone rubber layers comprise the runningsurface of the tread;

wherein rubber composition of the intermedial tread zone rubber layerhas a 100° C. hot rebound property greater than the 100° C. hot reboundproperty of the rubber composition of the lateral tread rubber layers;

wherein a path of least electrical resistance extends from said carbonblack-rich lateral rubber tread zone to the carbon black-rich tread baserubber layer by an extension of a lateral tread zone layer which extendsto and joins said tread base rubber layer or by an intermediate carbonblack-rich rubber bridge which extends between and joins said lateraltread zone rubber layer and said tread base rubber layer.

The silica rich rubber composition of the intermedial tread zone rubberlayer contains at least 40 phr of precipitated silica (syntheticamorphous precipitated silica) and a maximum of 30 phr of rubberreinforcing carbon black and is therefore relatively electricalresistive (relatively electrically non-conductive, relative to thecarbon black rich rubber compositions of the tread configuration).

The rubber reinforcing carbon black-rich rubber compositions of thelateral tread zone rubber layer, tread base rubber layer and rubberbridge (extending between said lateral tread zone rubber layer and saidtread base rubber layer to create the path of least electricalresistance) contains at least 40 phr of rubber reinforcing carbon blackand may also contain precipitated silica reinforcement.

Said silica reinforcement is used together with a silica coupling agentas will be hereinafter discussed.

In one embodiment, the value of the 100° C. hot rebound property of theintermedial tread zone rubber composition is at least about 4 unitsgreater than the 100° C. hot rebound property value of the stratifiedtread zone rubber composition.

For example, the 100° C. hot rebound value of the intermedial tread zonerubber composition may be in arrange of from about 60 to about 80percent and the 100° C. hot rebound value of the rubber composition ofthe tread zone rubber composition may be in a range of from about 56 toabout 76 so long as the 100° C. rebound values differ by at least about4 units (e.g. percentage units, for example, a hot rebound value of 80percent for the intermedial zone rubber composition and hot reboundvalue of 76 percent, or less, for the lateral tread zone rubbercomposition).

In one embodiment, it is further desired for the stratified lateraltread zone rubber composition to have a greater or equal, preferablygreater, tear resistance property than the intermedial tread zonerubber.

The elastomers of the rubber compositions of the intermedial treadrubber zone and lateral tread rubber zones may be the same or differentso long as the 100° C. hot rebound property of the rubber composition ofthe intermedial tread rubber zone is greater than the 100° C. hotrebound property of the rubber composition of the stratified lateralrubber zones.

For example, as hereinbefore discussed, the rubber composition of theintermedial zone is silica-rich in a sense of containing at least 40 phrof precipitated silica and a maximum of 30 phr of rubber reinforcingcarbon black so long as the 100° C. hot rebound property of theintermedial tread zone is greater than the 100° C. hot rebound propertyof the stratified tread zones.

For example, as hereinbefore discussed, rubber composition of thelateral tread lateral zones and tread base rubber layer are composed ofcarbon black-rich rubber compositions in a sense of containing at least40 phr of rubber reinforcing carbon black zones so long as the 100° C.hot rebound property of the intermedial tread zone is greater than the100° C. hot rebound property of the stratified tread zones.

In one embodiment, the span of the running surface of the intermedialtread zone rubber layer axially spans from about 30 to about 80 percentof the running surface of the tread cap rubber layer and the two lateraltread rubber zone rubber layers collectively span from about 20 to about70 percent of the running surface of the tread cap rubber layer wheresaid span of running surface of the tread includes the running surfacesof the tread lugs and widths of the tread grooves between the treadlugs.

In one embodiment, the span of the running surfaces of the twoindividual lateral tread zones may be of equal widths, or at least ofsubstantially equal widths, or may be asymmetrical in a sense that theyare of unequal widths, namely, for example, of widths within about 80 toabout 120 percent of each other.

As indicated, the span of the running surface of the tread cap layerincludes the outer running surface of the tread lugs (intended to beground contacting) and the width of the included grooves between thelugs.

In one embodiment, the Grosch abrasion rate (e.g. Grosch high abrasionrate) of the rubber composition of the running surfaces of theintermedial tread rubber layer and lateral tread zone rubber layers aredesirably similar. For example, in one embodiment their Grosch abrasionrates may be within about 5 to 20 percent of each other.

In one embodiment, the tear resistance (Newtons at 95° C.) of the rubbercomposition of the lateral tread zones is at least 20 percent greaterthan the tear resistance of the rubber composition of the intermedialtread zone.

In one embodiment, the lateral tread zones, intermedial tread zone andunderlying tread base are co-extruded together to form an integral andunified tread composite.

In one embodiment, the rubber composition of the intermedial, tread capzone has a lower tan delta value at 10 percent strain (100° C.) than therubber composition of the two lateral tread cap zones which ispredictive of lower hysteresis which is, in turn, predictive of lowerinternal heat buildup during tire service and a beneficially lowerrolling resistance contribution of the intermedial tread cap rubberlayer for the tire.

Accordingly, it is an aspect of this invention to provide a significantbalance of physical properties of rubber compositions between theintermedial tread zone and stratified lateral tread zones in a manner ofbeing a departure from past practice.

It is to be appreciated that one having skill in rubber compounding fortire treads can readily provide the tread zones with the indicatedrubber composition properties with routine experimentation and withoutundue experimentation.

BRIEF DESCRIPTION OF THE DRAWINGS

Drawings are presented as FIG. 1 (FIG. 1), FIG. 2 (FIG. 2), FIG. 3 (FIG.3) and FIG. 4 (FIG. 4) to provide a further understanding of theinvention.

FIG. 1 (FIG. 1) is provided to illustrate a partial cross sectional viewof a tire with a circumferential tread of a cap/base configuration wherethe outer cap rubber layer is divided into three circumferential treadzones.

FIG. 2 (FIG. 2) represents the tire of FIG. 1 with a path of leastelectrical resistance extending between a carbon black-rich lateraltread rubber zone and carbon black-rich tread base rubber layer.

FIG. 3 (FIG. 3) represents the tire of FIG. 1 with a path of leastelectrical resistance extending between a carbon black-rich lateraltread rubber zone and carbon black-rich tread base rubber layer.

FIG. 4 (FIG. 4) also represents the tire of FIG. 1 with a path of leastelectrical resistance extending between a carbon black-rich lateraltread rubber zone and carbon black-rich tread base rubber layer.

ADDITIONAL DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the tire with two spaced apart rubber reinforcingcarbon black-rich lateral tread zone rubber layers and a precipitatedsilica rich-intermedial tread zone rubber layer of which a portionextends in an axially outward direction from each side of theintermedial tread zone beneath the lateral tread zones and thereby joinsand separates the lateral tread zones from each other.

FIG. 2 illustrates the tire of FIG. 1 where the tread base rubber layeris an extension of the carbon black-rich lateral tread rubber zone.

FIG. 3 illustrates the tire of FIG. 1 where the path of least electricalresistance is comprised of a rubber reinforcing carbon black-rich rubberbridge component.

FIG. 4 also illustrates the tire of FIG. 1 where the path of leastelectrical resistance includes a rubber reinforcing black-rich rubberbridge component similar to FIG. 3 for which the tread base rubber layeris illustrated as extending beneath the carbon black-rich bridgecomponent and optionally axially outward to the outer surface of thetire sidewall.

The Drawings

In the Drawings, FIG. 1 illustrates a pneumatic tire partial crosssection (1) having a tread (2) of a cap/base configuration, namely anouter tread cap rubber layer (3) of a lug and groove configuration andan underlying tread base rubber layer (4). The outer tread cap rubberlayer (3) contains tread running surfaces (not numbered) contained onthe outer surfaces of the tread lugs of the tread (2) and is composed ofthree circumferential tread zones, each a part of the tread's runningsurface, comprised of a silica-rich intermedial tread zone rubber layer(6) between two spaced apart individual carbon black-rich lateral treadrubber zones (5A) and (5B) of which portions (6A) and (6B) of theintermedial tread zone (6) extend beneath and thereby underlie both ofthe lateral tread zones (5A) and (5B) and also overlay the carbonblack-rich tread base rubber layer (4). The outlying lateral tread zones(5A) and (5B) are thereby spaced apart from each other. The carbonblack-rich tread base rubber layer (4) thereby underlies the silica-richintermedial tread zone rubber layer (6) and is exclusive of the carbonblack-rich lateral tread zones (5A) and (5B). The lateral tread zones(5A) and (5B) are shown as being of the same width although they may beof widths which differ from each other.

The silica-rich rubber composition of the intermedial tread zone (6)contains at least 40 phr of precipitated silica reinforcement and amaximum of 30 phr of rubber reinforcing carbon black which thereforerenders the intermedial tread rubber composition electrically resistiverelative to carbon black-rich lateral tread zone rubber compositions.

The rubber reinforcing carbon black-rich rubber compositions of thelateral tread zones (5A) and (5B), tread base rubber layer (4) andsidewall rubber layer (9), as well as the bridging rubber component (10)shown in FIG. 3 and in FIG. 4, each contain at least 40 phr rubberreinforcing carbon black which renders them relatively less electricallyresistive, therefore relatively more electrically conductive, than therubber composition of the precipitated silica-rich intermedial treadrubber zone.

The tread lug and groove configuration of the tread cap rubber layerprovides tread lugs with intervening grooves with grooves (7) containedin the intermedial tread zone layer (6) and grooves (7A) and (7B)contained in the lateral tread zone layers (5A) and (5B) with each ofthe lateral tread zones thereby containing at least one tread groove.For such purpose, it is desired that the lateral tread zone layer rubbercompositions have a significantly greater tear resistance property thanthe intermedial zone layer rubber composition to thereby aid inprotecting the tread grooves (7A) and (7B) contained in the stratifiedlateral tread zone layers (5A) and (5B).

For FIG. 1, the intermedial tread zone (6) is depicted as constitutingabout 45 to 60 percent of the spanned running surface of the tire tread(2) and the two individual lateral tread zone layers (5A) and (5B) areof a substantially equal width and correspondingly collectivelyconstitute about 55 to about 40 percent of the spanned running surfaceof the tire tread (2). For exemplary FIG. 1, the intermedial andstratified lateral tread zone rubber compositions may be comprised ofthe same or different elastomers so long as the 100° C. hot reboundproperty of the intermedial zone rubber is greater than that of thestratified lateral zone rubbers.

As indicated, the span of the running surface of the tread cap layerincludes the outer running surface of the tread lugs (intended to beground contacting) and the width of the included grooves between thelugs.

For FIG. 2, a path of least electrical resistance is provided betweenthe carbon black-rich lateral tread rubber zones (5A) and 5(B) to thecarbon black rich tread base rubber layer (4) by an extension (8) oflateral tread rubber zones (5A) and (5B) which extends from the lateraltread zone to and joins the tread base rubber layer (4) and optionallyalso joins and overlays the carbon black-rich tire sidewall (9).

For FIG. 3 and FIG. 4, a path of least electrical resistance is providedbetween the carbon black-rich lateral tread rubber zones (5A) and 5(B)and the carbon black rich tread base rubber layer (4) by a carbonblack-rich bridge rubber component (10) which is positioned between andjoins the lateral tread rubber zones (5A) and (5B) and tread base rubberlayer (4).

FIG. 4 differs from FIG. 3 in a sense that the tread base rubber layer(4) extends axially outward beneath (and in contact with by joining) thebridge rubber component (10). For FIG. 4, the tread base rubber layer(4) is illustrated as extending axially outward beneath the bridgerubber component (10) to the outer surface of the tire sidewall (9).

For FIGS. 1, 2, 3 and 4, the tread base rubber layer (4) may, forexample, be primarily comprised of either cis 1,4-polyisoprene rubber,preferably natural rubber, or a combination of the cis 1,4-polyisoprenerubber and a polybutadiene rubber selected from cis 1,4-polybutadienerubber and trans 1,4-polybutadiene rubber. Optionally, also it may alsocontain up to about 20 phr (e.g. from about 5 to about 15 phr) of atleast one additional conjugated diene based elastomer such as, forexample, at least one additional diene-based elastomer selected from atleast one of styrene/butadiene rubber, isoprene/butadiene rubber, trans1,4-polybutadiene, low vinyl polybutadiene having vinyl content in arange of 10 to about 40 percent, and styrene/isoprene/butadiene rubber,preferably a styrene/butadiene copolymer rubber.

In practice, the coupling agent for the precipitated silicareinforcement of the respective zones of the tread may be, for example,an alkoxysilyl polysulfide such as for example, abis(3-trialkoxysilylalkyl)polysulfide wherein alkyl radicals for saidalkoxy groups are selected from one or more of methyl and ethylradicals, preferably an ethyl radical and the alkyl radical for saidsilylalkyl component is selected from butyl, propyl and amyl radicals,preferably a propyl radical and wherein said polysulfide componentcontains from 2 to 8, with an average of from 2 to 2.6 or an average offrom 3.5 to 4, connecting sulfur atoms in its polysulfidic bridge,preferably an average of from 2 to 2.6 connecting sulfur atoms to theexclusion of such polysulfides having greater than 2.6 connecting sulfuratoms.

Representative of such coupling agents are, for example,bis(3-triethoxysilylpropyl)polysulfide having an average of from 2 to2.6 or an average of from 3.5 to 4, connecting sulfur atoms in itspolysulfidic bridge, sometimes preferably an average of from 2 to 2.6connecting sulfur atoms to the exclusion of abis(3-triethoxysilylpropyl)polysulfide containing an average of greaterthan 2.6 connecting sulfur atoms in its polysulfidic bridge.

Such coupling agent may, for example, be added directly to the elastomermixture or may be added as a composite of precipitated silica and suchcoupling agent formed by treating a precipitated silica therewith or bytreating a colloidal silica therewith and precipitating the resultingcomposite.

In practice, the synthetic amorphous silica (precipitated silica) may beaggregates of precipitated silica, which is intended to includeprecipitated aluminosilicates as a co-precipitated silica and aluminum.

Such precipitated silica is, in general, well known to those havingskill in such art. For example, such precipitated silica may beprecipitated by controlled addition of an acid such as, for example,hydrochloric acid or sulfuric acid, to a basic solution (e.g. sodiumhydroxide) of a silicate, for example, sodium silicate, usually in thepresence of an electrolyte, for example, sodium sulfate. Primary,colloidal silica particles typically form during such process whichquickly coalesce to form aggregates of such primary particles and whichare then recovered as precipitates by filtering, washing the resultingfilter cake with water or an aqueous solution, and drying the recoveredprecipitated silica. Such method of preparing precipitated silica, andvariations thereof, are well known to those having skill in such art.

The precipitated silica aggregates preferably employed in this inventionare precipitated silicas such as, for example, those obtained by theacidification of a soluble silicate, e.g., sodium silicate and mayinclude co-precipitated silica and a minor amount of aluminum.

Such silicas might usually be characterized, for example, by having aBET surface area, as measured using nitrogen gas, preferably in therange of about 40 to about 600, and more usually in a range of about 50to about 300 square meters per gram. The BET method of measuring surfacearea is described in the Journal of the American Chemical Society,Volume 60, Page 304 (1930).

The silica may also be typically characterized by having adibutylphthalate (DBP) absorption value in a range of about 50 to about400 cm³/100 g, and more usually about 100 to about 300 cm³/100 g.

Various commercially available precipitated silicas may be consideredfor use in this invention such as, only for example herein, and withoutlimitation, silicas from PPG Industries under the Hi-Sil trademark withdesignations Hi-Sil 210, Hi-Sil 243, etc.; silicas from Rhodia as, forexample, Zeosil 1165MP and Zeosil 165GR, silicas from J. M. HuberCorporation as, for example, Zeopol 8745 and Zeopol 8715, silicas fromDegussa AG with, for example, designations VN2, VN3 and Ultrasil 7005 aswell as other grades of silica, particularly precipitated silicas, whichcan be used for elastomer reinforcement.

Representative examples of other silica couplers may beorganomercaptosilanes such as, for example, triethoxy mercaptopropylsilane, trimethoxy mercaptopropyl silane, methyl dimethoxymercaptopropyl silane, methyl diethoxy mercaptopropyl silane, dimethylmethoxy mercaptopropyl silane, triethoxy mercaptoethyl silane, andtripropoxy mercaptopropyl silane.

For this invention, it is desirable for physical properties of thesulfur cured rubber compositions of the tire tread zones to be aspresented in the following Table A.

TABLE A Intermedial zone rubber composition rebound At least 4 unitsgreater (Zwick) value (100° C.), as a percent than the rubber of thelateral tread zones Intermedial zone rubber composition Tan Delta Atleast 15 percent less value (1 Hertz, 15% strain, 100° C.) KPa than therubber of the lateral tread zones Lateral zone rubber composition tearAt least 20 percent resistance, 95° C., in Newtons greater than therubber of the intermedial tread zone

The tear resistance may be determined, for example, by ASTM D1876-1taken with DIN 53539 using a 5 mm wide tear width provided by alongitudinal open space, sometimes referred to as a window, cut orotherwise provided, in the film positioned between the two rubber testpieces where the window provides a geometrically defined area, namelythe tear width, for portions of two rubber test pieces to be pressed andcured together after which the force to pull the test pieces apart ismeasured.

In practice, the invention the rubber compositions for the tire treadcomponents may be prepared in a sequential series of at least twoseparate and individual preparatory internal rubber mixing steps, orstages, in which the diene-based elastomer is first mixed with theprescribed carbon black and/or silica in a subsequent, separate mixingstep and followed by a final mixing step where curatives are blended ata lower temperature and for a substantially shorter period of time.

It is conventionally required after each mixing step that the rubbermixture is actually removed from the rubber mixer and cooled to atemperature of less than 40° C. and, for example, in a range of about40° C. to about 20° C. and then added back to an internal rubber mixerfor the next sequential mixing step, or stage.

The forming of a tire component is contemplated to be by conventionalmeans such as, for example, by extrusion of rubber composition toprovide a shaped, unvulcanized rubber component such as, for example, atire tread. Such forming of a tire tread is well known to those havingskill in such art.

It is understood that the tire, as a manufactured article, is preparedby shaping and sulfur curing the assembly of its components at anelevated temperature (e.g. 140° C. to 180° C.) and elevated pressure ina suitable mold. Such practice is well known to those having skill insuch art.

It is readily understood by those having skill in the art that therubber composition would be compounded by methods generally known in therubber compounding art, such as mixing the various sulfur-vulcanizableconstituent rubbers with various commonly used additive materials, asherein before discussed, such as, for example, curing aids such assulfur, activators, retarders and accelerators, processing additives,such as rubber processing oils, resins including tackifying resins,silicas, and plasticizers, fillers, pigments, fatty acid, zinc oxide,waxes, antioxidants and antiozonants, peptizing agents and reinforcingmaterials such as, for example, carbon black. As known to those skilledin the art, depending on the intended use of the sulfur vulcanizable andsulfur vulcanized material (rubbers), the additives mentioned above areselected and commonly used in conventional amounts.

Typical amounts of fatty acids, if used which may be comprised ofstearic acid which may also contain at least one of palmitic and oleacacids, may comprise about 0.5 to about 3 phr. Typical amounts of zincoxide comprise about 1 to about 5 phr. Typical amounts of waxes, ifused, comprise about 1 to about 5 phr. Often microcrystalline waxes areused. Typical amounts of peptizers, if used, comprise about 0.1 to about1 phr. Typical peptizers may be, for example, pentachlorothiophenol anddibenzamidodiphenyl disulfide.

The vulcanization is conducted in the presence of a sulfur vulcanizingagent. Examples of suitable sulfur vulcanizing agents include elementalsulfur (free sulfur) or sulfur donating vulcanizing agents, for example,an amine disulfide, polymeric polysulfide or sulfur olefin adducts.Preferably, the sulfur vulcanizing agent is elemental sulfur. As knownto those skilled in the art, sulfur vulcanizing agents are used in anamount ranging from about 0.5 to about 4 phr, or even, in somecircumstances, up to about 8 phr, with a range of from about 1.5 toabout 2.5, sometimes from about 2 to about 2.5, being preferred.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve the properties of the vulcanizate. Inone embodiment, a single accelerator system may be used, i.e., primaryaccelerator. Conventionally and preferably, a primary accelerator(s) isused in total amounts ranging from about 0.5 to about 4, preferablyabout 0.8 to about 2.5, phr. In another embodiment, combinations of aprimary and a secondary accelerator might be used with the secondaryaccelerator being used in smaller amounts (of about 0.05 to about 3 phr)in order to activate and to improve the properties of the vulcanizate.Combinations of these accelerators might be expected to produce asynergistic effect on the final properties and are somewhat better thanthose produced by use of either accelerator alone. In addition, delayedaction accelerators may be used which are not affected by normalprocessing temperatures but produce a satisfactory cure at ordinaryvulcanization temperatures. Vulcanization retarders might also be used.Suitable types of accelerators that may be used in the present inventionare amines, disulfides, guanidines, thioureas, thiazoles, thiurams,sulfenamides, dithiocarbamates and xanthates. Preferably, the primaryaccelerator is a sulfenamide. If a second accelerator is used, thesecondary accelerator is preferably a guanidine, dithiocarbamate orthiuram compound.

The mixing of the rubber composition can preferably be accomplished bythe aforesaid sequential mixing process. For example, the ingredientsmay be mixed in at least three stages, namely, at least twonon-productive (preparatory) stages followed by a productive (final) mixstage. The final curatives are typically mixed in the final stage whichis conventionally called the “productive” or “final” mix stage in whichthe mixing typically occurs at a temperature, or ultimate temperature,lower than the mix temperature(s) of the preceding non-productive mixstage(s). The terms “non-productive” and “productive” mix stages arewell known to those having skill in the rubber mixing art.

Example I

Proposed rubber compositions were prepared for use for the intermedialand lateral tread zone rubber layers for the tire of this invention. Theproposed intermedial tread zone rubber composition is referred in thisExample as rubber Sample A.

The proposed lateral tread zone rubber composition is referred in thisExample as rubber Sample B.

The basic rubber composition formulations are shown in Table 1 and theingredients are expressed in terms of parts by weight per 100 partsrubber (phr) unless otherwise indicated.

The rubber composition may be prepared by mixing the elastomers(s)without sulfur and sulfur cure accelerators in a first non-productivemixing stage (NP-1) in an internal rubber mixer, for example, for about4 minutes to a temperature of, for example, of about 160° C. If desired,the rubber mixture may then mixed in a second non-productive mixingstage (NP-2) in an internal rubber mixer, for example, for about 4minutes to a temperature of, for example, about 160° C. with or withoutadding additional ingredients. The resulting rubber mixture may then bemixed in a productive mixing stage (PR) in an internal rubber mixer withsulfur and sulfur cure accelerator(s), for example, for about 2 minutesto a temperature of, for example, about 110° C. The rubber compositionmay then sheeted out and cooled to, for example, below 50° C. betweeneach of the non-productive mixing steps and prior to the productivemixing step. Such rubber mixing procedure is well known to those havingskill in such art.

The following Table 1 presents basic rubber formulations for proposedintermedial tire tread zone (rubber Sample A) and peripheral tire treadzone (rubber Sample B) rubber compositions for the zoned tread of thisinvention.

TABLE 1 (Intermedial and Lateral Tread Cap Zones) Parts (phr) A(Intermedial) B (Lateral) Non-productive Mix Step (NP1) Natural cis1,4-polyisoprene rubber 35 35 (TTR20) Cis 1,4-polybutadiene rubber¹ 6565 Carbon black (N121) 35 35 Silica, precipitated² 15 15 Silica couplingagent³ 2 0 Composite of silica coupling agent and 0 2 carbon black(50/50 weight ratio)*⁴ Wax microcrystalline and paraffin 1.5 1.5 Fattyacid⁵ 2 2 Antioxidants 4 4 Zinc oxide 3 3 Final Mix Step (PR) Sulfur 1.10.9 Accelerator(s)⁶ 1.6 1.5 *Therefore 1 phr of coupling agent and 1 phrrubber reinforcing carbon black. ¹Cis 1,4-polybutadiene rubber (saidorganic solvent solution polymerized 1,3-butadiene monomer in thepresence of a neodymium catalyst) as CB25 ™ from the Lanxess Companyhaving a Tg of about −105° C. and heterogeneity index in a range of fromabout 1.5/1 to about 2.2/1 ²Precipitated silica as Zeosil ™ Z1165 MPfrom the Rhodia Company ³Silica coupling agent comprised ofbis(3-triethoxysilylpropyl) polysulfide having an average of from about2 to about 2.6 connecting sulfur atoms as Si266 ™ from Evonic ⁴Compositeof silica coupling agent and carbon black (carrier) in a 50/50 weightratio where said coupling agent is comprised ofbis(3-triethoxysilylpropyl) polysulfide having an average of from about2 to about 2.6 connecting sulfur atoms as Si266 ™ from Evonic ⁵Mixturecomprised of stearic, palmitic and oleic acids ⁶Sulfenamide withdiphenyl guanidine sulfur cure accelerators with retarder as needed

The following Table 2 represents the uncured and cured behavior andvarious physical properties of the rubber compositions for theintermedial (rubber Sample A) and lateral (rubber Sample B) tire treadzone rubber layers based upon the basic formulations illustrated inTable 1.

TABLE 2 Properties A (Intermedial) B (Lateral) RPA (Rubber ProcessAnalyzer) test¹ Dynamic storage modulus (G′) Cured rubber G′ (1 Hertz,10% strain, 1.79 1.49 100° C.), KPa Tan delta (1 Hertz, 10% strain, 100°C.) 0.091 0.122 Stress-strain, ATS² Tensile strength (MPa) 21.2 20.8Elongation at break (%) 461 529 300% modulus, ring, (MPa) 12.1 9.66Rebound (Zwick)  23° C. 59 55 100° C. 69 64 Shore A Hardness  23° C. 6563 100° C. 61 58 Tear strength (tear resistance)³, 88 121 N at 95° C.Abrasion rate (mg/km), 369 368 Grosch⁴ high severity (70 N), 12° slipangle, disk speed = 20 km/hr., distance = 250 meters ¹RPA, rubberproperty analytical instrument ²Automated Test System instrument (ATS),Instron Corporation, which incorporates a number of tests in oneanalytical system and reports data from the tests such as, for example,ultimate tensile strength, ultimate elongation, modulii and energy tobreak data. ³Data obtained according to a tear strength (peal adhesion),or tear resistance test. The tear resistance may be determined by ASTMD1876-01 taken with DIN 53539 using a 5 mm wide tear width provided by alongitudinal open space, sometimes referred to as a window, cut orotherwise provided, in the film positioned between the two rubber testpieces where the window provides a geometrically defined area, namelytear width, for portions of two rubber test pieces to be pressed andcured together after which the ends of the two test pieces are pulledapart at right angles (90° + 90° = 180° to each other) and the force topull the test pieces apart is measured. An Instron instrument may beused to pull the rubber pieces apart using an Instron instrument at 95°C. with the force required being reported as Newtons force. ⁴The Groschhigh severity abrasion rate may be conducted on an LAT-100 Abrader andis measured in terms of mg/km of rubber abraded away. The test rubbersample is placed at a slip angle under constant load (Newtons) as ittraverses a given distance on a rotating abrasive disk (disk from HBSchleifmittel GmbH). In practice, a high abrasion severity test may berun, for example, at a load of 70 Newtons, 12° slip angle, disk speed of20 km/hr and distance of 250 meters.

It is seen in Table 2 that the Experimental rubber Sample A (rubbercomposition proposed for the intermedial tread zone) and Experimentalrubber Sample B (rubber composition proposed for the lateral treadzones) fulfilled the beneficially desired physical propertyrelationships presented in Table A for 100° C. hot rebound, and tearresistance (95° C.) values.

In Table 2 it is seen that the rebound value for rubber Sample A(proposed intermedial tread zone rubber composition) was greater thanthe for rubber Sample B (proposed peripheral tread zone rubbercomposition) which is indicative of beneficially lower hysteresis whichin turn is predictive of a beneficially lower rate of internal heatgeneration in the intermedial tread zone rubber composition as well aspredictively beneficial reduction of rolling resistance for the tirewith a resulting predictive fuel economy for a vehicle using such tires.

Further, in Table 2 it is seen that tear resistance for rubber Sample B(proposed lateral tread zone rubber composition) was beneficiallysignificantly greater than for rubber Sample A (proposed intermedialtread zone rubber composition).

Further, it is seen in Table 2 that the high severity Grosch rates ofabrasion for both rubber Sample A (proposed intermedial tread zonerubber) and rubber Sample B (lateral tread zone rubber) are similar,which is a desirable feature.

Further, it is seen in Table 2 that the tangent delta (tan delta) valuefor rubber Sample B (proposed lateral tread zone rubber) is greater thanfor rubber Sample A (proposed intermedial tread zone rubber). Such tandelta properties, taken with the aforesaid rebound properties, are afurther indication of lower hysteresis, lower internal heat generationduring tire service for the intermedial tread rubber zone as well as theaforesaid predictive beneficial promotion of reduction in tire rollingresistance for increased vehicular fuel economy.

In summary and conclusion, a tire is provided with a configuredcircumferential tread zones to provide a running surface with zoneshaving similar rates of abrasion resistance but with lower hysteresis inthe intermedial tread zone which extends axially outward beneath thehigher hysteresis lateral tread zones for a purpose of maximizing suchlower hysteresis for the tread and with a higher tear resistance for thelateral tread rubber zone to promote resistance to groove surfacecracking in tread groove(s) contained in the lateral tread zones.

Such innovative tread configuration is intended to promote lower rollingresistance for the tire tread across the width of the tread by theextended intermedial tread zone which extends axially outward beneaththe lateral tread zones and to beneficially promote tear resistance forthe outlying lateral tread zones, the combination of which is consideredto be a significant departure from past practice.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

What is claimed is:
 1. A tire is provided having a circumferentialrubber tread composed of a cap/base configuration comprised of an outertread cap rubber layer with a lug and groove configuration with theouter portions of the tread lugs providing the running surface of thetread, and a tread base rubber layer underlying the outer tread caprubber layer; wherein the outer tread cap rubber layer is composed ofthree circumferential load bearing zones comprised of a silica-richintermedial tread zone rubber layer positioned between and extendingbeneath two carbon black-rich lateral tread zone rubber layers tothereby underlie the lateral tread zone rubber layers and overlay thecarbon back-rich tread base rubber layer; wherein outer tread lugsurfaces of the intermedial tread zone rubber layer and the lateraltread zone rubber layers comprise the running surface of the tread;wherein rubber composition of the intermedial tread zone rubber layerhas a 100° C. hot rebound property greater than the 100° C. hot reboundproperty of the rubber composition of the stratified lateral treadrubber layers, wherein a path of least electrical resistance extendsfrom said carbon black-rich lateral rubber tread zone to the carbonblack-rich tread base rubber layer by an extension of a lateral treadzone layer which extends to and joins said tread base rubber layer or byan intermediate carbon black-rich rubber bridge which extends betweenand joins said lateral tread zone rubber layer and said tread baserubber layer, wherein the silica-rich rubber composition of theintermedial tread zone rubber layer contains at least 40 phr ofprecipitated silica and a maximum of 30 phr of rubber reinforcing carbonblack and is therefore relatively electrical resistive, wherein therubber reinforcing carbon black-rich rubber compositions of the lateraltread zone rubber layer, tread base rubber layer and rubber bridgecontains at least 40 phr of rubber reinforcing carbon black.
 2. The tireof claim 1 wherein the value of the 100° C. hot rebound property of theintermedial tread zone rubber composition is at least about 4 unitsgreater than the 100° C. hot rebound property value of the lateral treadzone rubber composition.
 3. The tire of claim 1 wherein the 100° C. hotrebound value of the intermedial tread zone rubber composition is inarrange of from about 60 to about 80 percent and the 100° C. hot reboundvalue of the rubber composition of the lateral tread zone rubbercomposition is in a range of from about 56 to about 76 so long as the100° C. rebound values differ by at least about 4 units.
 4. The tire ofclaim 1 wherein the lateral tread zone rubber composition has an atleast 20 percent greater tear resistance property than the intermedialtread zone rubber and where the intermedial and lateral tread zones areconfigured with lugs and intervening grooves with each lateral treadzone containing at least one tread groove.
 5. The tire of claim 1wherein the elastomers of the rubber compositions of the intermedialtread rubber zone and lateral tread rubber zones are the same ordifferent so long as the 100° C. hot rebound property of the rubbercomposition of the intermedial tread rubber zone is greater than the100° C. hot rebound property of the rubber composition of the lateralrubber zones.
 6. The tire of claim 1 wherein the span of the runningsurface of the intermedial tread zone rubber layer axially spans fromabout 30 to about 80 percent of the running surface of the tread caprubber layer and the two lateral tread rubber zone rubber layerscollectively span from about 20 to about 70 percent of the runningsurface of the tread cap rubber layer where said span of running surfaceof the tread includes the running surfaces of the tread lugs and widthsof the tread grooves between the tread lugs.
 7. The tire of claim 6wherein the span of running surfaces of the two individual lateral treadzones are of substantially equal widths.
 8. The tire of claim 6 whereinthe span of running of the two individual lateral tread zones isasymmetrical in a sense that they are of unequal widths.
 9. The tire ofclaim 1 wherein the Grosch high severity abrasion rate of the rubbercompositions of the running surfaces of the intermedial tread zonerunning surface and lateral tread zone are desirably similar.
 10. Thetire of claim 1 wherein the lateral tread zones, intermedial tread zoneand underlying tread base are co-extruded together to form an integraland unified tread composite.
 11. The tire of claim 1 wherein the rubberof the intermedial, tread cap zone has a lower tan delta value at 10percent strain (100° C.) than the rubber of the two lateral tread capzones.
 12. The tire of claim 1 wherein the tear resistance (Newtons at95° C.) of the rubber composition of the lateral tread zone rubber is atleast 20 percent greater than the tear resistance of the rubbercomposition of the intermedial tread zone.
 13. The tire of claim 1wherein the intermedial and lateral tread zones are configured with lugsand intervening grooves with the lateral tread zones each containing atleast one tread groove.